Free Flaps

ETIOLOGY AND INCIDENCE OF FREE FLAPS

Femtosecond LASIK

A free flap or a cap is a rare but significant complication that can occur with femtosecond LASIK. This can happen during flap manipulation rather than during flap creation. Following its creation, the corneal flap can be inadvertently severed from the hinge in the process of lifting, positioning, and refloating. On occasion, a tear may happen at the hinge leading to a free flap. Risk factors include the following:

Tight adherence of the flap to the closed lid speculum due to flap dehydration resulting from a longer than typical procedure.
A thin corneal flap.

Some of the potential complications of free flap include irregular astigmatism, recurrent flap dislodgement, and complete flap loss. Studies show a rate of less than 0.5% of true free flap during femtosecond LASIK.^1,2

Microkeratome LASIK

A free flap results from unintended complete dissection of the corneal flap. Flat corneas (K < 42 diopters [D]) are more prone to this complication. Often, a free flap is thinner than intended. Intraoperative factors leading to a free flap include the following:

Inadequate suction ring placement.
Lack of synchronization between translational keratome movement and oscillatory blade movement.
Malposition and misadjustment of the thickness foot-plate or the “stop” mechanism during assembly of microkeratomes (early models of certain horizontal microkeratomes eg, Bausch + Lomb’s ACS keratome).
Microkeratome jam, preventing microkeratome head reversal to free the cap. This might prompt the surgeon to release the suction, thus lifting the instrument with an incarcerated flap, resulting in a free flap.

The reported incidence of true free flap during micokeratome LASIK ranges from 0.01% to 1% in large sample studies.3

FEMTOSECOND LASIK COMPLICATIONS AND IMMEDIATE SOLUTIONS

Complication #1: Free Flap

Video section: 0 minutes 26 seconds

Platform: IntraLase FS60 kilohertz (kHz) (Abbott Medical Optics)

Flap diameter: 9.3 mm

Flap target depth: 90 microns (µm)

The initial surgery on the right eye resulted in air bubbles in the anterior chamber. Radial gentian violet marks were applied using an optical zone marker at the intersection of the flap edge and corneal bed. The flap was carefully lifted, and excimer laser ablation was applied. In the process of repositioning the flap back onto the ablated corneal bed, its tight adherence to the lid speculum resulted in a full-thickness detachment of the flap from its superior hinge (video 6; time: 0 minutes 26 seconds; Figures 6-1, 6-2, 6-3, 6-4, 6-5, 6-6, and 6-7).

Some practical measures are as follows:

Reposition the free flap using the fiduciary marks.
Place a 10-0 nylon suture at the 9 o’clock position with an air knot to minimize any torque, irregular astigmatism, or decentration tension.
Place a contact lens.